Interference suppressor for internal combustion engines



June 22, 1965 L. TEXSIER BJQLB?) INTERFERENCE SUPPRESSOR FOR INTERNAL COMBUSTION ENGINES Filed Sep't 5, 1961 A TTORNE YS 3,191,133 yINTERFERENCl) SUPPRESSOR FOR INTERNAL COMBUSTIGN ENGNES Lon Texsier, 21 Rue du Pont Neuf, Paris, France Filed Sept. 5, 1951, Ser. No. 135,973

Claims priority, application France, Apr. 25, 1961,

859,839 3 Claims. (Cl. S33-79) An ignition system for an internal combustion engine constituted by a contact breaker, a coil, a distributor and a sparking plug may be considered as a generator of damped electrical oscillations, the frequencies of which extend over a range of values which is ill-defined by reason of the complexity of the different parameters involved.

In fact, the frequency band of the oscillations produced when the spark jumps across the electrodes of the plug (acting as a negative resistance) may extend to several megacycles according to the values of the distributed capacities and the inductance value of each constituent member of the ignition system and the assembly thereof.

Apart from this, other oscillations, the frequencies of which are to be found in a range of values ranging from a few megacycles to several hundreds and probably several thousands of megacycles, are produced as a result of the excitation of the connections of the ignition system interconnecting the different members, particularly the connections connecting the distributor head to the plugs and that connecting this head to the coils. Such an excitation comes from the production of steep-fronted oscillations produced when the jumping of the spark between the electrodes of the plug is begun and finished.

Also the connections near the ignition system, such as those connecting the battery and the headlamps in an -automobile vehicle, for example, are in their turn excited in the same way and produce parasitic oscillations.

The total result of the parasitic oscillations thus produced causes considerable disturbance when radio electrical waves are received and this happens in extremely extended frequency band values.

Numerous means intended to reduce the effects of the disturbance phenomena have already been proposed. But in actual fact it is found that if these known means do allow a suppression to be achieved which is generally more satisfactory the greater its complexity, they jeopardize the ignition conditions for the plug.

Up to now all the known and used systems may be substantially placed in two categories:

(l) The one which makes use either of the integral screening of the entire ignition system of the engine (aircraft etc.) or the partial screening of members (connectors, cables etc.).

(2) The other which makes use of the introduction into the circuits of damping members, that is to say more or less virtual resistances or inductances Apart from the integral screening method which stems from a kdifferent and particularly expensive technique, the

` other solutions cannot be considered as usefully efficient from the point of view of suppression for a sufficiently large frequency band and are not entirely free from the production of interference during the actual ignition process itself.

The present invention has for an object to make a suppressor device of the second category mentioned above, designed so as simultaneously to obtain an efficient suppression for a very large range of frequencies and conditions favorable to ignition while retaining a retail price allowing yit to be extensively applied to all types of vehicles. y f

The invention is based on the fact that the residual United States Patent O 3,l9l,i33 Patented June 22, 1965 capacity of many types of plugs in current use is of a very substantially constant value of the average order of l5 ,ufarad.

The principle from which the invention comes consists in using this residual capacity as an active member of the suppressor device instead of considering it as an inevitable parasitic part.

A suppressor device according to the invention intended to be directly inserted between the plug, having a determined residual capacity Cbg, and the plug lead, also by construction having a determined capacity C4, is characterized in that it is constituted by a low pass T-tilter network, this network on the one hand comprising, in series, two assemblies resistor R1 and inductance 'and resistor R2 and inductance L2 respectively formed by a resistance R1 or R2 in series with an inductance L1 or L2 and on the other hand, in shunt, a capacity of value C3 which is in the neighborhood of the value of the residual capacity Chg of the plug, these values of the different aforementioned parameters being interconnected by the following relationships:

KRW/Off@ the values of the resistance being expressed in ohms, those of the capacities in farads and those of the inductances in henrys.

In fact it is found that, by reason of its direct insertion between the plug with the residual capacity Chg, and the plug lead with a capacity C4, the low pass T-lter network in fact, by reason of the presence of these capacities Chg and C4, forms an assembly which from the point of View of electrical operation is equivalent to the connection in series of two low pass 1r-ltens. The first of these networks is constituted by the series arrangement R1, L1 and the shunt arrangement of the capacitative members Chg and C2. The second of these net-works is constituted of the tseries assembly R2L2 and of the capacitative members C3 and C4 in shunt, the capacity C3 thus being common to tlhe two networks.

It should be noted that the constitution of these filter networks of a suppressor device according to the invention stems from two interconnected physical principles.

In the first place these filter networks -are low-pass networks, the voltage attenuation of which, as a function of the frequency, is, as calculus shows, 12 decibels per octave per network. As in this case we are dealing with ya pulse carrier wave with a very large frequency range conducted via the filters to the input of a connection, the other end of which is open, it may be lseen that this oscillation .'will pass through four networks in a to and fro movement which gives an attenuation of 48 decibels per ocatve beyond the individual cut-off frequency of the networks.

-V dam-ping conditions obtain; i l i' i lIn the second place, these filters, the relative values of theelenients of which are determined in order to form av critical damping, have the property of transformingv thev i pulse signal appearing at the terminals of the plug at the ,i

shape there is once more to be found a strong limitation of its frequency range in relation to the pulsev produced v by the plug.

During this time, and this is essential, for here is shown an improvement inignition, the current 'ofthe spark of the plug due to this phenomenon vwill have been ex-Y ponentiallyl decreasing without oscillations as in the oase ofra direct connection and thus withnosuccesive passing through cancellations withf'al reversal of direction. In

other words the energy provided tothe plug will,l from the moment 'at which the spark jumps, have been` unij formly'decreaising and will becancelled only once. When the sparkv stops, [a new pulse signal appears; the ilatter,

with -a voltage which is much lower' than the rst, will beVA rapidly Vabsorbed ina to and fro movement without there taking place any spark between the ,electrodes or"V the plug; In order that the inventionmay be more clearly under;

stood, reference will now be made -to Vthe accompanyingv t dnawings which show some embodiments thereof byway of example and in which:

FIGURE l shows anj electrical circuit diagram of a suppressor device according to the present invention, and' FIGURES 2 to 4, by way of example, show different ,embodiments of tihe actual device.

Referring first to FIGURE 1 in this drawing have been diagrammatioally shown the electrodes Bg of the plug, the residual capacity of the latter being denoted Yby Chg.

The actual suppressor device directly inserted between the plug and the plug lead is shown inside broken` lines,

and is made up of the` low'pass T-f'lter network corn-i prising, in series, the resistance R1=inductance L1 and Y resistance R2=inductance L2 and, in shunt, 4the capacity The plug leadris represented by its equivalent 'circuit comprising the capacity C4 and the resistancefR4. The capacity C4 is that `of this conductor` in relation to earth and the resistance Rgis the 'equivalent resistance of the j leakages by radiation and ohmic resistance.

The method of operation of the `device is as follows:

when the spark is jumpingthe terminals of the electrodes Y of the plug Bg, the` pules wave which is produced on these electrodes first of allpasses through theassembly of the members R1, L1 and C3 and then reaches the input of thel tirst passage through the members R1, L1 and 'C3'under-- goes considerable weakening of its high frequency components in such a way that, for the components of the low frequencies,A the plug lead at its i-nputconsti'tutes a capaci-Y tative member. The high frequency components` of the range al-though .weakened `.undergo reecti'on at the other endof the conductor and return.r Itimay be seen'that the reflected wave must pass through the first assembly-L2, R2 and1C3 and then the second .assembly L1, R1 andCbg.YV 'Mathematical study shows that itis necessary thaty the values of theV different members aresuoh that the three adjacentrmembers R, L, .C consider-edin'ia tilter'have `an extravoltage comprisedv between 0.7 (a value for/Which"` the amplitude/inequencyv ycurve of thev assembly iR, L,.CV y is always decreasing) fandi0.5, a Value'lfor which criticalV l In other words oneshould have ythe following relationships: n y :(Il) Since Cb.g is an imposed value equal on average `to ,iL/.ufaradz l this latterfrelationship 'being automatically veried if itbe y very little diterent from rthat of Chg. '(3) Finally .another group of conditions which may be termed fnon resonance, due tothe capacities placed in series in pairs, impose: i. Y

f All the above mathematical constructions thus allow the values ofi-each of the constituent members-of the Ifilters to be yprecisely determined. 40 For example, inva particular Acase the following numeri- Ical values willbe obtained i Y Y Cba=12 /L/f- R1'=1.400o i 1:20 ph. Y with acap-acity of the assembly R1. and L1 in relation to earth lower Ithan 05h/tf. i 03:14 ,tf. R2='1.400S2 Y 1 Y Mh. with acapacity of the assembly R2and L2 in relation to earth lower than`0.5 auf. f Y

In the embodimentsshown by way of example in FIG- UR-ES-Z and 3, themernbers ycomprising resistor R1 and inductance L1and resistor R2 and inductance L2 are lformed by windn'g'a resistant wire lon to a core `1 of suitable insulating material which simultaneous-ly allows the intended'values `for R and L of each of the networks of the filter to be obtained, that is tosayy an inductance and a resistance formed .according tothe above relationships. Inrthe niiddle of theY core is ar flange 2 on whichy is mounted ametal ring 3 (or alternativelyl the Harige .2 may be metallized), and would thus 'constitute oneof Ethe ele-ctrodes'of thecapacity C3.. At the-same time, the ring 3 4tllls the role of a lossless screen between two coils which :are thus not coupled..` Y l i These coils are mounted in the body of a connector 4 of plas-tic material which is suitable by reason of its dielectric qualities (rigidity :and permanence), the outside 6 of `*which* is either metallized by a' knownmethod or insertedin a metal envelope and this forms the second electrode Aofthe'capacity C3. This conductive portion, to-

on therbody kof.' the plug, ensures the electrical Iearth get-herwith-adeviceg'S ensuring' the nonfinductive .contact return .common to the assembly of the elements of the filters.

The other portions of this embodiment, eg. iixation on the output electrode of the plug, the output of the cable etc., :are conventional.

In another embodiment the assembly of the suppressor device is mounted directly in the body of a plu-g, as shown in EIGURE 4. In this figure the same reference numerals indicate the same members as in FIGURES 2 and 3.

I claim:

1. An interference suppressor device for internal combustion engines, for direct insertion between the sparkplug, which has a determined residual capacity Cbg, and the plug lead, which has a determined capacity C4, said suppressor device being constituted by a low pass T-lter network, said network on the one hand comprising, in series, two assemblies resistor R1 and inductance L1 and resistor R2 and inductance L2 respectively formed by a resistance R1 or R2 in series with an inductance L1 or L2 and on the other hand, in shunt, a capacity of value C3 near to the value of the residual capacity of the plug Chg, the Values of the different aforementioned parameters being interconnected by the following relationships:

and also preferably 'me values of the resistances being expressed in ohms, those of the capacities in farads and those ofthe inductances in henrys.

2. A device as claimed in 1, in which: the two members resistor R1 and inductance L1 and resistor R2 and inductance L2 are made in the form of two coils on a core of insulating material, having a support between the coils for a metal ring or a metallized layer constituting one of the electrodes of the capacity C3, the other terminal of this capacity :being made in the form of the outer metallisation of a connector of insulating material inside which is located the aforementioned core.

3. A device as claimed in claim 2, in which said connector is a unitary part of said spark plug.

References Cited by the Examiner UNITED STATES PATENTS 1,723,908 8/29 Alexanderson 333-79 1,946,680 2/34 Franklin 333-79 1,984,526 12/34 Gwen 123148 2,238,915 4/41 Peters 333-81 2,322,773 6/43 Peters 174-119 2,894,221 7/59 Coy S33-79 3,002,126 9/61 Noir 315-58 HERMAN CARL SAALBACH, Primary Examiner. 

1. AN INTERFERENCE SUPPRESSOR DEVICE FOR INTERNAL COMBUSTION ENGINES, FOR DIRECT INSERTION BETWEEN THE SPARK PLUG, WHICH HAS A DETERMINED RESIDUAL CAPACITY CBG, AND THE PLUG LEAD, WHICH HAS A DETERMINED CAPACITY C4, SAID SUPPRESSOR DEVICE BEING CONSTITUTED BY A LOW PASS T-FILTER NETWORK, SAID NETWORK ON THE ONE HAND COMPRISING, IN SERIES, TWO ASSEMBLIES RESISTOR R1 AND INDUCTANCE L1 AND RESISTOR R2 AND INDUCTANCE L2 RESPECTIVELY FORMED BY A RESISTANCE R1 OR R2 IN SERIES WITH AN INDUCTANCE L1 OR L2 AND ON THE OTHER HAND, IN SHUNT, A CAPACITY OF VALUE C3 NEAR TO THE VALUE OF THE RESIDUAL CAPACITY OF THE PLUG CBG, THE VALUES OF THE DIFFERENT AFOREMENTIONED PARAMETERS BEING INTERCONNECTED BY THE FOLLOWING RELATIONSHIPS: 